This is only my second jam game, but with my game, You have One Shot, I made a script that applied a pitch shift and low pass filter to all of the sound based on the time slowing down and removing it when you speed back up! Alongside that I spent a good few hours working on sound effects and music for the game with Air Hybrid 3 ;)
https://itch.io/jam/gmtk-2019/rate/462609
(The time slows down when you jump ;) )